This invention relates to a process for the preparation of a laminate of a textile substrate and an integral polyvinyl fluoride film layer on at least one surface of the substrate.
A process for making an integral polyvinyl fluoride film was discussed in U.S. Pat. No. 2,953,818 which issued to L. R. Barron on Sept. 27, 1960. This patent claims a process for producing polyvinyl fluoride film from a mixture of finely-divided polyvinyl fluoride particles and a latent solvent for the particles. The solvent is removed to produce a gel which is then cured. The produced film structures are self-supporting and capable of being oriented.
Polyvinyl fluoride films have been used for many years by printed circuit board manufacturers as a release agent in the manufacture of epoxy and phenolic printed circuit boards. Production rates of such circuit boards were increased by use of these films because of the films' high-temperature tolerance and non-stick properties. Since the desirable release-agent properties are imparted by the fluoropolymer surface, it would be advantageous if there could be provided a tough, durable, relatively low cost carrier for the fluoropolymer surface that would impart improved handling properties beyond those of self-supporting polyvinyl fluoride film.
Known bonding of such polyvinyl fluoride film to a textile substrate as in U.S. Pat. No. 3,265,556 which issued to Hungerford et al. on Aug. 9, 1966 is not practical from an economic viewpoint, since polyvinyl fluoride film is not commercially available in web thicknesses of less than about 0.5 mil. The manufactured cost of such a laminate would, therefore, be too high. Also, the commercially available polyvinyl fluoride film is oriented which results in a film that is too stiff, has low tear strength and is prone to shrink when subjected to heat.
U.S. Pat. No. 3,360,396, which issued to Kennedy et al. on Dec. 27, 1967, discloses a substrate coating process wherein a polyvinyl fluoride-latent solvent dispersion is applied onto the surface of the substrate to give a wet coating thickness of up to about 30 mils thickness and subsequently heated to effect adhesion of the coating to the substrate. The casting of such a solvent solution of the polyvinyl fluoride polymer onto a textile substrate with the subsequent removal of the solvent does not provide a practical method for making a coated textile product. This is because polyvinyl fluoride is insoluble in commonly used volatile solvents such as acetone, petroleum ether, isooctane, xylene, carbon tetrachloride, chloroform, methanol, ethanol, etc., and polyvinyl fluorides of high inherent viscosity (high molecular weight), which are preferred for film manufacture, are less soluble even in hot solvents such as hot dimethylformamide, tetramethylene sulfone, nitroparaffins, cyclohexanone, dibutyl ketone, mesityl oxide, aniline, phenol, methyl benzoate, phenyl acetate and diethyl phosphate than are the polyvinyl fluorides of lower inherent viscosity. While the use of hot solutions to accomplish solvent casting techniques is possible, it presents serious equipment and safety problems. Such a process also produces a coated textile substrate that is quite thick and stiff. In fact, such a laminate is too thick and stiff for use as a release film in the manufacture of printed circuit boards.
Canadian Pat. No. 1,076,015, which issued on Nov. 4, 1974, describes a process for coating a plastisol (with plasticizer) of polyvinyl chloride or a copolymer of vinyl chloride with vinyl acetate as a cohesive gel onto a fabric and then curing the resulting laminate. Apparently, such processes have not been used with polyvinyl fluoride. Polyvinyl chloride is much less costly than polyvinyl fluoride, so that a greater degree of impregnation of a textile substrate by the gelled coating can be tolerated with polyvinyl chloride. It could be anticipated that too much polyvinyl fluoride would impregnate such a substrate for economical results, especially since polyvinyl fluoride is used without plasticizers.
This invention provides a practical method for preparing a coated textile substrate having a thin integral coating of polyvinyl fluoride polymer on at least one surface of the substrate. It has been found that quite thin layers of polyvinyl fluoride can be made to stay on the surface of a textile substrate.